1. Technical Field
The present invention relates to cooling-fan motors and impellers that are used in electronic devices and the like. More specifically, the present invention relates to fan motors that must generate high static pressure and ample airflow volume, and to cantilever-type impellers that are used in such fan motors.
2. Description of the Related Art
FIG. 8 is a plan view of a conventional centrifugal fan motor. FIG. 9 is a vertical cross section along the line X1-O1-Y1-Z1 in FIG. 8. This centrifugal fan motor includes a motor component 104 for generating rotational driving force, an impeller component 101 for generating airflow, and a housing 106. This centrifugal fan motor has a rotational axis O1 shown in FIG. 8.
The impeller component 101 is located around the outer periphery of the motor component 104 and includes a lower end wall 102 and blades 103. The lower end wall 102 is an annular plate member located surrounding the motor component 104 at a lower position in the axial direction, and lies in a plane perpendicular to the rotational axis. The lower ends of the blades 103 are fixed to the surface of the lower end wall 102 at its outer radial margin. The blades 103 are supported only by the lower end wall 102, which structure is called as cantilever structure. When the motor component 104 rotates in the normal direction, the blades 103 generate an airflow in the direction indicated by the arrow B1. In the direction indicated by the arrow A1, an intake airflow through an air inlet 108 is generated by the sucking action of this airflow B1. On the other hand, in the direction indicated by the arrow C1, an ejection airflow is generated by the blowing action of the airflow B1.
In configuring the impeller component 101 of conventional centrifugal fans used for electronic devices and the like, the tendency is to make the blade diameter 2r1 greater than the height h1, where 2r1 represents the diameter of the blades 103 to their outer perimeter and h1 represents the height of the blades 103 in the axial direction. One of the purposes of adopting this structure is to save space in the axial direction. Another purpose for thus having the blade diameter be greater than the height h1 is to improve air volume and static pressure of the ejection airflow C1 by raising the rotational speed at the periphery of the blades 103. Therefore, in the conventional centrifugal fan having a cantilever impeller for cooling electronic devices and the like, the impeller has a low-profile configuration in which the relationship h1≦2r1 holds.
In this conventional centrifugal fan, the intake airflow A1 pushes on the airflow B1 as indicated in FIG. 9, and the airflow B1 strikes downward on the lower end wall 102 because of the shorter height h1 of the blades, which results in a large windage loss between the downward airflow and the wall surface of the lower end wall 102. This is why, in considering the distribution of wind speed measured at several observation locations corresponding to points along the rotational axis of the impeller component 101, the wind speed of the intake airflow within the impeller tends to be maximal at the upper surface of the lower end wall 102 of the impeller. The windage loss on the wall surface can decrease airflow volume from the fan and lower the cooling efficiency below the inherent performance of the fan motor.
Meanwhile, electronic devices recently are being made smaller and smaller so as to be suitable for carrying, as is the case with cellular phones, mobile personal computers, and other devices that call for being downsized further. At the same time, integration of electronic circuits has been enhanced and circuit processing speeds have been increased, which has led to a tendency for the total amount of heat produced by LSI chips and embedded electronic circuitry to increase. Therefore, there is a need to realize a fan motor having not only a smaller size but also higher cooling efficiency.